Ophthalmic lenses

ABSTRACT

The present invention relates to the use of metal organic compounds in a process for providing a moulded plastic article comprising the step of polymerization casting of a curable composition comprising one or more polymerizable molecules or compounds or compositions in the presence of a mould release agent, which in turn comprises a metal organic compound, complexes and/or salts thereof. Such use leads to less surface defects of the moulded article and lower mould damage.

The present invention relates to a process for providing molded plasticarticles, in particular ophthalmic lenses, plastic articles andophthalmic lenses themselves, and the use of metal organic compounds insuch processes.

Recently, organic glass has begun to replace inorganic glass in opticalelements, such as windows, prisms, cameras, television screens,telescopes, and ophthalmic lenses. The term ophthalmic lenses refers tocorrective lenses as well as non-corrective lenses such as sunglasses.Organic glass possesses several favourable characteristics, including alighter weight and better safety, e.g., better impact resistance, thaninorganic glass.

Conventional materials used in organic glass include polystyrene resin,polymethyl methacrylate resin, and polycarbonate resin. However, thesepolymers have their respective disadvantages. For example, polymethylmethacrylate resin is liable to high moisture absorption, which changesits shape and refractive index. Also, polystyrene resin andpolycarbonate resin have the disadvantage of giving rise tobirefringence, light scattering, and loss of transparency with time.Furthermore, polymethyl methacrylate and polystyrene are neither scratchnor solvent resistant.

Organic glass made up of the products of the radical polymerization ofpoly(allyl carbonates) of polyhydroxy alcohols is also known, forexample from European patent application 0 473 163. These polymers donot have the above-mentioned problems. However, when applying poly(allylcarbonates) of polyhydroxy alcohols in ophthalmic lenses increased moulddamage occurs. Understood by mould damage is the damage incurred in alens or in a mould on opening of the mould wherein the lens is formed.

Another known problem of such lenses is the occurrence of a surfacedefect of the casted organic glass that is known as “ferns”. The defectsare called this way because they always appear in the shape of a fernleaf. The exact nature of these ferns and how they are being formed isunknown, but since the size of such ferns can vary from 0.5 to 30 cm²,they pose a real problem. It is possible to remove said ferns from thesurface by polishing, however, such a process is undesired.

A further known problem is the uneven tinting of casted lenses with acolouring agent by means of a process of imbibing the lens, suchprocesses being well-known in the art. The fact that the lens iscoloured unevenly, may be associated with surface defects as well. Aprocess wherein lenses are coloured more evenly is desired.

The Japanese patents JP 238151 and JP 09241336 teach the use ofphosphorous compounds (phosphorous being a group 15 element according tothe new IUPAC notation, with an electronegativity of about 2.1) as mouldrelease agents. Common release agent present a number of problems whenapplied in the manufacturing of optical articles such as ophthalmiclenses. They regularly require high amounts to be effective and therebynegatively effect the mechanical and optical performance of the castedmaterial. Furthermore they negatively affect the surface tension of thepolymer, making the application of a coating (anti-scratch or othercoating) and evenly tinting very difficult and its performanceunreliable.

WO 96/24865 from the applicant teaches the use of diallyl phthalate typeoligomers in curing compositions for ophthalmic lenses whereby moulddamage in the production of said lenses is reduced.

Moulds used in today's industry to prepare ophthalmic lenses frompoly(allyl carbonate) of a polyhydroxy alcohol are only suited forcompositions which result in ophthalmic lenses with identical refractiveindices. A change in refractive index will result in a change in powerof the lens when utilizing these moulds. Compositions resulting inhigher refractive index lenses will require different moulds to obtainophthalmic lenses with the same power. So, improvement of the propertiesof lenses by introducing certain oligomers and, optionally, comonomerscannot be achieved without limiting the refractive index of theresulting lens so that the moulds do not have to be changed.

An object of the present invention is to provide a process for providingmoulded plastic articles whereby the mould damage, the occurring offerns (ferning) and other tinting failures are being reduced.

The present invention relates to a process for providing a mouldedplastic article comprising the step of polymerization casting of acurable composition comprising one or more polymerizable molecules orcompounds which are preferably radically polymerizable and arepreferably monomers, co-monomers and/or oligomers, for examplepoly(allyl carbonates) of polyhydroxy alcohols and methacrylic, acrylic,vinylic or allylic comonomers, in the presence of a mould release agent,which in turn comprises a metal organic compound, complexes and/or saltsthereof, with the proviso that the metal of the metal organic compoundis not Si or P. It is understood that the term metal as used here alsoincludes transition elements. Furthermore it is noted that the term“radical polymerizable monomers” does not comprise conventional monomersthat lead to urethane formation. Preferably, the invention relates tothe process in which essentially all monomers are radicallypolymerizable. More preferably, the process involves the polymerizationof a composition which consists essentially of radically polymerizablemonomer(s), initiator(s), tinting agent(s), and the metal organiccompound.

The mould damage, and ferns or other tinting failures in the productionof the ophthalmic lens according to the present invention by using theclaimed metal organic compounds is reduced without adversely affectingmechanical and/or optical properties of the optical articles, such ashardness and refractive index. Furthermore these metal organic releaseagents do not substantially negatively effect the surface tension of thepolymer and monomer, and hence do not substantially negatively effectthe adhesion of (anti-scratch) coatings onto the polymer surface.Preferred metal organic compounds are selected from organometalliccompounds, complexes of metals, metal salts, and metal soaps. Mostpreferred are organometallic compounds wherein the metal is covalentlybonded. The valency of the metal will typically vary from 1-6, a valencyof 2-6 being preferred. Preferred metal organic compounds are of theformulae 1-111

wherein M is the metal as defined, X=O or S, and R¹-R⁸ are independentlyselected from the group consisting of hydrogen, halogen, hydrocarbyl,halogen substituted hydrocarbyl, and

wherein R⁹ is C₂-C₂₂ hydrocarbyl, preferably C₄₋₁₂ hydrocarbyl, and Xhas the meaning as defined above,

whereby R¹-R⁸ are optionally connected to form a ring structure.

Preferred compounds have a structure wherein R¹-R⁸ are independentlyselected from essentially hydrogen, halogen, octoate, laurate, butyl,hexanoate, and decanoate. More preferred compounds are dibutyl metaldilaurates, dibutyl metal oxides, and metal 2-ethylhexanoates(octoates).

Without wishing to be bound to such theory, it appears that theelectronegativity of the metal is an important factor for selectingmetal organic compounds that are useful in the process according to theinvention. Using the table of electronegativity of elements ascalculated according to Allred & Rochow and as published in the textbookby Cotton & Wilkinson in Basic Inorganic Chemistry, ISBN# 0471-50532 3,Table 2-3, as a reference, the preferred metal of the metal organiccompound has an electronegativy from 1.5 to 1.75. More preferred metalshave an electronegativity, as calculated by Allred & Rochow's method, of1.6 to 1.73. Most preferred metals are Zn, Sn, and Co.

If used to produce ophthalmic lenses, the metal organic release agentsmust be completely soluble in the monomer to prevent the reduction oftransmission of the lens.

The inventors have noted that the claimed metal organic compoundsexpress release agent activity even at very low concentration, and aresuitable as both internal, i.e. present in the polymerizablecomposition, release agents and external, i.e. applied directly to themould, release agents. Preferably, the metal organic compounds are usedas an internal release agent

If used as an external release agent, they may be applied to the mouldprior to lens casting, for example, by any suitable methods such asspraying or dipping, either in the concentrated form, or as a solutionin a solvent. Typically, if applied as a solution, the solvent isallowed to evaporate before the mould is actually used in the castingprocess.

If used as an internal release agent, the metal organic compounds can beintroduced in the polymerizable composition in the pure form or asdissolution in a suitable medium. Such suitable medium is typically onemonomer, or a mixture of monomers, to be used in the polymerizablecomposition. Although it is possible to combine the pure metal organiccompound with other compounds (in the pure form) that are to be used inthe composition, such as e.g. the initiator or the colouring agent, thisis typically not desired since the metal organic compounds may have adestabilizing effect on such compounds, which may lead to hazardoussituations. Preferably, the metal organic compounds are introduced intothe polymerizable composition in the pure form or in the form of saiddissolution in one or more monomers. For accurate dosing it is preferredto use a solution of the metal organic compound with a concentration of0.001 to 50% w/w. More preferably 0,01 to 25% w/w, and even morepreferably 0.05 to 20% w/w. Such solutions may supply all of the monomerto be polymerized, or, preferably, be combined with further monomer.

The metal organic compounds according to the invention are not meant tobe used as radiation shielding compounds as described in, for instance,U.S. Pat. No. 5,856,415. Whereas radiation shielding compounds aretypically used in an amount of greater than 15% by weight (% w/w) inorder to be effective, the mould release agents are typically used inlower concentration. More preferably they are used in a concentration ofless than 10% w/w, while most preferably they are used in an amount ofless than 5% w/w. All based on the weight of the final lens.

Preferably, the metal organic compounds are used in such a quantity thatthe surface tension of the finished product is about equal to thesurface tension of the mould that is used. More preferably, the surfacetension of the mould is less than 37 mN/m to prevent the defects asdescribed above from occurring. In case the casting composition is usedin the casting of ophthalmic lenses using glass moulds, it is preferredto use the metal organic release agent in an amount such that themaximum required force to open the mould is 200N or less. Morepreferably, the required mould opening force is less than 90N, while amaximum force of 80N is most preferred. Another way to establish thedesired amount of metal organic compounds in the ophthalmic lens castingprocess is by evaluation of the demoulding energy that is released uponopening of the mould. Preferably, the amount is chosen such that thedemoulding energy is less than 0.15 Nm, more preferably less than 0.1Nm. Typically the metal organic compound is used in a quantity from0.0001 (1 ppm) to 5% w/w, more preferably 0.001 to 2% w/w, even morepreferably 0.002 to 1% w/w, and most preferably 0.0025 to 1% w/w, basedon the total weight of the casted composition.

The radical polymerizable molecules or compounds can be generallypolymerized by either a method in which the polymerization isaccomplished with heat or a method in which the polymerization isaccomplished with light. As radical polymerizable monomers there can beused any widely known monomer having a radical polymerizing groupwithout limitation.

Further radically polymerizable monomers may optionally be present inthe curable composition up to 20% w/w. These comonomers may bemethacrylic, acrylic, vinylic or allylic. Examples include methylacrylate, methyl methacrylate, phenyl methacrylate, vinyl acetate, vinylbenzoate, diallyl isophthalate, diallyl terephthalate, diallyl adipate,and triallyl cyanurate.

The compositions of the present invention will typically contain apolymerization initiator in quantities ranging from 0.01 to 10 wt % asis known in the art. This initiator should be soluble in the othercomponents present in the composition to be cured and capable ofproducing free radicals at a temperature which ranges from 30° toapproximately 100° C. Examples of such initiators are organic peroxideand percarbonate initiators, especially diisopropyl peroxydicarbonate,dicyclohexyl peroxydicarbonate, di-sec-butyl peroxydicarbonate,dibenzoyl peroxide, tert-butyl perbenzoate, benzoyl peroxide, laurylperoxide, azobis(iso-butylonitrile) andazobis(2,4di-methylvaleronitrile). For the purpose of the presentinvention, it is preferable for the polymerization initiator to bepresent in the composition in quantities from about 1 to 8% w/w Theinitiators can be used either singly or in combination of two or more.

The curing of the polymerizable composition of the present invention canalso be conducted by using a conventional photo polymerizationinitiator. As the photo polymerization initiator, any widely knowncompound can be used without limitation that is added forphotopolymerizing the radical polymerizable monomers. Examples of thephotopolymerization initiator that can be used in the present inventionare Acetophenone initiators, such as1-phenyl-2-hydroxy-2-methylpropane-1-one, hydroxycyclohexylphenylketone; Acylphosphine oxide initiators such as 2, 4,6-trimethylbenzoyidiphenylphosphine oxide,2,6-dichlorobenzoyidiphenyl-phospineoxide; Bisacylphosphine oxideinitiators and dicarbonyl compounds.

The poly(allyl carbonates) of polyhydroxy alcohols may be used in theform of either monomers or oligomers and are of the conventional type.Monomers are usually obtained by using chloroformates. In this way,diethylene glycol diallyl carbonate can be obtained by reactingdiethylene glycol bis(chloroformate) with allyl alcohol in the presenceof an alkali, as described in Kirk-Othmer, Encyclopedia of ChemicalTechnology, 3rd ed., John Wiley & Sons, 1978, Vol. 2, p. 111. Monomersand oligomers of poly(allyl carbonates) of polyhydroxy alcohols can alsobe suitably obtained by means of transesterification reactions betweendiallyl carbonate and a polyhydroxy alcohol, as described in Europeanpatent application 0 035 304. In this way, monomers or mixtures ofmonomers and oligomers can be obtained, depending on the ratio ofdiallyl carbonate reagents to polyhydroxy alcohol. It is also possibleto obtain mixed poly(allyl carbonates) of polyhydroxy alcohols byreacting a diallyl carbonate with a mixture of polyhydroxy alcohols in atransesterification reaction. These mixed poly(allyl carbonates) ofpolyhydroxy alcohols are also included in the present invention.Monomers of poly(allyl carbonates) of potyhydroxy alcohols are preferredfor the ophthalmic lens of the present invention.

The polyhydroxy alcohols used in the preparation of poly(allylcarbonates) of polyhydroxy alcohols contain from 2 to 20 carbon atomsand from 2 to 6 hydroxy groups in the molecule. Examples of thesealcohols are: ethylene glycol, diethylene glycol, triethylene glycol,tetraethylene glycol, 1,3-propylene glycol, 1,4-butanediol,1,6-hexanediol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol,1,4-dimethanol cyclohexane, 4,8-bis(hydroxyethyl) tricyclo(5,2,1,0^(2,6))decane, α,α′-xylenediol, 1,4-bis(hydroxyethyl) toluene,2,2-(bis(4-hydroxyethyl)phenyl) propane, pentaerythritol, trimethylolpropane, dipentaerythritol, ditrimethylol propane, andtris(hydroxyethyl) isocyanurate. The following polyhydroxy alcohols arepreferred: diethylene glycol, 1,4-dimethanol cyclohexane,pentaerythritol, and tris(hydroxyethyl) isocyanurate.

Examples of the diol include ethylene glycol, 1,2-propylene glycol,1,4-butanediol, 1,6-hexanediol, 1,4-dimethanol cyclohexane,1,3-butanediol, neopentyl glycol, 1,3-cyclohexanediol, p-xylene glycol,and styrene glycol, and other aliphatic and aromatic diols. Brancheddiols are preferable to linear ones. Examples of such branched diolsinclude 1,2-propylene glycol, 1,3-butanediol, neopentyl glycol,2,3-butanediol, 1,4-pentanediol, 1,3-pentanediol, 1,2-pentanediol,2,3-pentanediol, 2,4-pentanediol, 1,5-hexanediol, 1,4-hexanediol,1,3-hexanediol, 1,2-hexanediol, 2,3-hexanediol, 2,4-hexanediol,2,5-hexanediol, and 3,4-hexanediol.

Examples of the polyols include aliphatic trihydric alcohols, such asglycerine and trimethylol propane, and aliphatic polyhydric alcohols,such as pentaerythritol and sorbitol.

Examples of polymerizable monomers that can favorably be used in thepresent invention include the following compounds of the conventionaltype.

That is, polyfunctional acrylate or methacrylate, such as diethyleneglycol dimethacrylate, triethylene glycol dimethacrylate and2,2-bis(4-methacryloyloxyethoxyphenyl)propane. Examples of other radicalpolymerizable monomers include unsaturated carboxylic acids such as(meth)acrylic acid, maleic anhydride, (meth)acrylic ester compounds suchas methyl(meth)acrylate, benzyl(meth)acrylate, bisphenol-Adi(meth)acrylate, urethane (meth)acrylate and epoxy(meth)acrylate; allylcompounds such as diallyl phthalate, diallyl terephthalate, diallylcarbonate and allyl diglycol carbonate; aromatic vinyl compounds such asstyrene, α-methylstyrene, vinyl naphthalene, and divinylbenzene;cyclohexyl diallyl ester oligomers, diallyl phthalate ester oligomers,and diallyl terephthalate ester oligomers. These monomers may be used ina single kind or being mixed together in two or more kinds.

For the production of ophthalmic lenses it is preferred to use a castingcomposition resulting in a lens with a refractive index of 1.45 to 1.55,more preferably 1.48-1.52, most preferably about 1.5.

The composition may also contain one or more conventional additives toact as ultraviolet light absorbers, dyes, pigments, and/or infraredlight absorbers.

FIG. 1 is a tensile-elongation diagram with the force necessary to pulltwo glass plates away from each other plotted against percentage ofextension.

The invention will be further illustrated by the following examples.

Mould damage occurs by adhesion of the cured polymer to the glass mould.It is possible to measure the adhesion of the cured polymer to the glasswith the aid of a tensile tester. To this end a monomer composition ispolymerized between two parallel, degreased glass plates, havingdimensions of 30×8 cm which are held together with a PVC-ring. Afterpolymerization, the PVC-ring is removed and the top glass plate ispulled loose on the short side on the tensile tester at 60° C. Thisgives a tensile-elongation diagram as shown in the accompanying FIG. 1,with the force necessary to pull the two glass plates way from eachother plotted against the percentage of extension.

A good parameter for the adhesion to the glass mould is the overallrelease energy (E-total). This is the surface area under theabove-mentioned diagram.

Examples 1 to 6 and Comparative Examples A to G

A clear homogeneous solution was obtained by mixing diethyleneglycolbisallyl carbonate (Nouryset 2000® ex. Akzo Nobel), organometalliccompounds and 2.7% w/w of diisopropyl peroxy dicarbonate (IPP), thewhole mixture being 100%. The mixture was degassed at 20 mbar for 15minutes until gas evolution stopped. The glass mould assemblies werefilled with the mixture. Polymerization took place in an oven with apolymerization cycle of 21 hours at a temperature rising exponentiallyfrom 45° to 80° C.

In comparative Examples B to G instead of the organometallic compounds,Lauric acid or Zelec® UN, a commercially available phosphate esterrelease agent for thermosetting applications ex DuPont, were used.

Table 1 lists the compositions which have been polymerized, mentioningthe amount of organometallic compound present in the composition and theproperties of the resulting lenses, Barcol hardness, the F-open (Fmax),the E-total (Etot) and the Tinting hardness. Throughout the examples theamount as specified is the amount of the indicated compound based on thetotal weight of the composition.

TABLE 1 examples according to the present invention: Barcol TintingMetallic Amount Fmax Etot hardness hardness Tinting failure Lenscompound (ppm) (N) (N) (%) (%) (%) A none 0 129 0.25 31 ± 2 45 ± 330-50% 1 DBTL 160 58 0.020 30 ± 2 43 ± 2 not measured 2 DBTO 40 76 0.02031 ± 2 49 ± 2 not measured 3 Sn-octoate 160 88 0.11 not measured 47 ± 2not measured 4 DBTL 40 70 0.040 30 ± 2 41 ± 2 not measured 5 DBTL 20 790.070 30 ± 2 42 ± 2 not measured 6 DBTL 10 86 0.080 30 ± 2 45 ± 2 notmeasured 7 DBTL 90 0-6% Key to table 1: DBTO — Di butyl tin oxide(Tegokat ® 248 ex Goldschmidt) DBTL — Di butyl tin dilaurate (Tegokat ®218 ex Goldschmidt) Sn-octoate — Tegokat ® 129 ex Goldschmidt

Tinting Hardness

A useful method for the measurement of the hardness of optical polymersis the standard tinting test. To tint a sample, 1.51 g Terasil® Rot R isdissolved in 800 ml demineralized water. The (blanco) transmission of atest piece at 500 nm is measured. Then the test piece is immersed during4 minutes in the tinting bath at 92-94° C. after which the sampleimmediately is dipped in cold water to stop the pigment impregnationcompletely. After cleaning the test piece with EtOH, the transmission ofthe test piece after tinting is measured at 500 nm. The tinting hardnessis now calculated according to the following formula:

 T _(n)=(T _(t) /T _(b))* 100%

T _(n)=tinting hardness (%)

T _(b)=transmission at 500 nm of test piece before tinting

T _(t)=transmission at 500 nm of test piece after tinting

The results in Table 1 for E-total show that the lenses comprising thecompositions of the present invention will result in a significantreduction of demoulding energy, and hence a reduction of mould damage,even at very low concentration of organometallic compound withoutadversely affecting other properties such as Barcol hardness and Tintinghardness.

Tinting failures are seen when tinted lenses exhibit so called “whitearches” and “ferns”, defects which seriously impair the quality of thelenses.

The results in table 2 show that the organometallic compounds will notnegatively effect the coatability of the (polymer) lens, because they donot negatively influence the surface tension of polymer. Furthermore,organometallic compounds decrease the surface tension of the glass mold,thereby facilitating the demoulding process.

TABLE 2 Examples according to the present invention: Lens Glass Metal-Surface mould lic Amount tension Surface tension Lens compound (ppm)(mN/m) (mN/m) A none  0 37 ± 2 47 ± 2 1 DBTL 160 35 ± 2 33 ± 2 2 DBTO 40 35 ± 2 35 ± 2

Comparative Examples B to G

Compositions were prepared according to the procedure mentioned in

Examples 1 to 6. The results are listed in Table 3.

TABLE 3 Comparative examples Com- Amount Fmax Etot Lens pound (ppm) (N)(Nm) B Lauric acid 40 111 0.21 C Lauric acid 20 108 0.23 D Lauric acid10 109 0.24 E Zelec UN 100   70 0.090 F Zelec UN 50  79 0.14 G Zelec UN25  86 0.16

The results in Table 3 show that common release agents (Zelec UN) areless effective as release agent than the organometallic compounds of thepresent invention. Furthermore, it is also shown that the organo part ofan organometallic compound (lauric acid) by itself does not expressrelease agent properties.

Examples 8-10 and Comparative Example H

In the process as described for Example 1, various metal organic releasecompounds were evaluated with the following results:

Ex- am- Com- Amount Fmax Etot Barcol T ple pound (ppm) (N) (N) hardness(%) H none — 124-144 0.27-0.30 34 ± 2 93.2  8 Zn-octoate 140  58 0.03 32± 2 93.0  9 Mn-octoate  30 113 0.26 31 ± 2 93.1 10 Co-octoate  30  930.23 35 ± 2 92.4 T = transmittance Zn-octoate = Zn-2-ethylhexanoate(Durham ®-Zinc (2) ex Elementis) Mn-octoate = Mn-2-ethylhexanoate(Durham ®-Manganese ex Elementis) Co-octoate = Co-2-ethylhexanoate(Durham ®-Cobalt ex Elementis)

Clearly, these metal organic compounds improve the demoulding of thelens from the mould.

Example 11 and Comparative Example I

In a process according to example 1, the amounts of ferns in castedlenses were evaluated. When no metal organic compound was used, about40% of all lenses possessed ferns. However, using 50-100 ppm(0.005-0.01% w/w) of DBTL resulted in a reduction of ferns so that lessthan about 10% of all lenses contained ferns.

Example 12-16

In the process of Example 1, further tin compounds were evaluated withthe following results:

Ex- am- Com- Amount Fmax Etot Barcol T ple pound (ppm) (N) (N) hardness(%) H none — 124-144 0.27-0.30 34 ± 2 93.2 12 DBSnDA 238 45 0.01 31 ± 293.0 13 BSnTO 225 69 0.04 34 ± 2 93.2 14 MBSnO 141 96 0.19 33 ± 2 93.015 TASn 107 80 0.18 32 ± 2 93.0 16 EncDBTDL 222 61 0.08 34 ± 2 91.3 T =transmittance DBSnDA = Dibutyltindiacetate (Tegokat ® 233 exGoldschmidt) BsnTO = Butyltintris(2-ethylhexanoate)(Tegokat ® 220 exGoldschmidt) MBSnO = Monobutyltinoxide(Tegokat ® 256 ex Goldschmidt)TASn = Tetraallyltin (ex Aldrich) EncDBTDL = Encapsulated DBTDL(Intelimer ® 5012 ex Landec)

The use of the compounds led to improved demoulding and less surfacedefects such as ferning and uneven tinting. Various other tin compoundswere evaluated with similar results, demonstrating that it is the metalthat is decisive in obtaining the desired positive effects in thecasting operations. The organic part of the metal organic compound,however, may be optimized to increase performance. Most likely this isrelated to the differences in solubility in the total compositionbecause of the differences in organic groups.

The invention is not limited to the above description, the requestedrights are rather determined by the following claims.

What is claimed is:
 1. A process for preparing ophthalmic lensescomprising the steps of: polymerizing a polymerizable composition in thepresence of a mould release agent in a casting mould; the mould releaseagent comprising at least one of: a metal organic compound, a metalorganic complex, and a salt thereof, wherein the metal of the mouldrelease agent has an electronegativity of 1.5 to 1.75, when calculatedaccording to the method of Allred and Rochow, and is not Si or P;opening the casting mould to release an ophthalmic lens; and imbibingthe ophthalmic lens, after releasing from the casting mold, in a tintingsolution to recover a tinted ophthalmic lens substantially free ofsurface defects including ferns and tinting failures.
 2. The processaccording to claim 1, wherein the mould release agent is used in anamount sufficient to lower the force required to open the mould to lessthan 200N.
 3. The process according to claim 1, wherein the mouldrelease agent is used in an amount of 0.0001 to 1% by weight, based onthe weight of a total composition.
 4. The process according to claim 1,wherein the metal organic compound is selected from the group consistingof the formula I-III:

wherein M is the metal as defined, X=O or S, and R¹-R⁸ are independentlyselected from the group consisting of hydrogen, halogen, hydrocarbyl,halogen substituted hydrocarbyl, and

wherein R⁹ is C₂-C₂₂ hydrocarbyl, and X has the meaning as definedabove, whereby R¹-R⁸ are optionally connected to form a ring structure.5. The process according to claim 4, wherein R¹-R⁸ of the metal organiccompound are selected from the group consisting of octoate, laureate,butyl, hexanoate, and decanoate and wherein the metal (M) is Sn or Zn.6. The process according to claim 1, wherein the metal organic compoundis selected form the group consisting of dibutyl metal dilaurates,dibutyl metal oxides, and metal 2-ethylhexanoates (octoates).
 7. Anophthalmic lens obtainable according to the process of claim
 1. 8. Theprocess according to claim 1, wherein the metal of mould release agenthas an electronegativity of 1.6 to 1.73 when calculated according to themethod of Allred and Rochow.
 9. The process according to claim 1,wherein the mould release agent is used in an amount sufficient to lowerthe force required to open the mould to less than 90 N.
 10. The processaccording to claim 1, wherein the mould release agent is used in anamount sufficient to lower the demoulding energy that is released uponopening of the mould to less than 0.15 Nm.
 11. The process according toclaim 1, wherein the mould release agent is used in an amount sufficientto lower the demoulding energy that is released upon opening of themould to less than 0.10 Nm.
 12. The process according to claim 1,further comprising the step of adding the mould release agent in thepolymerizable composition prior to the polymerizing step.
 13. Theprocess according to claim 1, further comprising the step of applyingthe mould release agent in the mould prior to the polymerizing step. 14.The process according to claim 1, wherein the mould is made of glass.15. The process according to claim 4, wherein R⁹ is C₄₋₁₂ hydrocarbyl.16. A process for preparing ophthalmic lenses comprising the steps of:polymerizing a polymerizable composition in the presence of a mouldrelease agent in a casting mould; the mould release agent comprising ametal organic compound, wherein the metal of the mould release agent hasan electronegativity of 1.5 to 1.75, when calculated according to themethod of Allred and Rochow, and is not Si or P, wherein the metalorganic compound is selected from the group consisting of the formulaI-III:

wherein M is the metal as defined, X=O or S, and R¹-R⁸ are selected fromthe group consisting essentially of hydrogen, halogen, octoate,laureate, butyl, hexanoate, and decanoate, and releasing an ophthalmiclens from the casting mould.
 17. The process according to claim 16,wherein the metal (M) is Sn or Zn.
 18. The process according to claim16, wherein the metal organic compound is selected form the groupconsisting of dibutyl metal dilaurates, dibutyl metal oxides, and metal2-ethylhexanoates (octoates).
 19. The process according to claim 16,wherein the mould release agent is added to the casting mould, prior tothe polymerizing step.
 20. The process according claim 16, wherein themould release agent is added to the polymerizable composition, prior tothe polymerizing step.
 21. The process according to claim 16, whereinthe mould release agent is used in an amount of 0.0001% to 1% by weight,based on the weight of a total composition.
 22. The process according toclaim 16, wherein the mould is made of glass.
 23. The process accordingto claim 16, further comprising the step of imbibing the ophthalmic lensin a tinting solution to recover a tinted ophthalmic lens substantiallyfree of surface defects including ferns and tinting failures.
 24. Anophthalmic lens obtainable according to the process of claim 16.